This application claims priority to Japanese Patent Application No. JP-2001-367028 filed on Nov. 30, 2001.
1. Field of the Invention
The present invention relates to an unwanted peak detection apparatus for detecting unwanted peaks caused by antenna sidelobes or harmonics from among peak data output from a radar apparatus and, in particular, from a millimeter-wave radar apparatus.
2. Description of the Related Art
Using millimeter-wave radar (FM-CW radar), the distance to a target located in the path ahead and the relative velocity of the target can be measured at the same time. Further, by scanning the radio wave projection direction, the angle at which the target is located can be determined and, based on the angle, the lateral position of the target can be determined.
However, because of the characteristics of millimeter-wave radar, when a target having a large reflected power is present, the target may be detected in the direction of an angle different from the angle where it should be, due to a sidelobe of the radio wave radiated from the antenna. As no actual target is present at the angle defined by the sidelobe, the result obtained using the peak associated with the sidelobe is a false target, leading to the occurrence of a ghost or an erroneous calculation of the lateral position of the real target.
Further, because of the characteristic of millimeter-wave radar, when a target having a large reflected power is present, a pseudo-reflection due to a harmonic occurs, as a result of signal saturation, in the same angle direction as that of the reflection from the real target. As, usually, no target is present at the position of the harmonic, the result obtained using the peak associated with the harmonic is a false target and appears as a ghost.
An object of the present invention is to provide an apparatus for detecting unwanted peaks such as a peak due to a sidelobe and a peak due to a harmonic.
According to the present invention, there is provided an unwanted peak detection apparatus for detecting an unwanted peak, from among peaks output from a radar apparatus, and having a frequency and an angle, as parameters indicating peak positions, comprising: means for determining a main peak having an intensity greater than a predetermined threshold value; means for searching for a peak within a region having a predetermined positional relationship with respect to the position of the main peak; and means for determining whether a found peak is an unwanted peak or not, by using a criterion dependent on the intensity of the main peak.
In one example, the searching means searches for the peak within a range where frequency is substantially equal to the frequency of the main peak and where an angle difference relative to the main peak is substantially equal to an angle corresponding to a sidelobe of an antenna of the radar apparatus.
In another example, the searching means searches for the peak within a range where angle is substantially equal to the angle of the main peak and where the frequency is substantially equal to an integral multiple of the frequency of the main peak.